1. Field of the Invention
The present invention relates to a solid composite material where fine particles of a crystalline metal carbonate are dispersed in an organic matrix at the nano level and a method of producing the same.
2. Background of the Invention
Crystals of a metal carbonate such as calcium carbonate are superior in strength and thus attracting attention as high-strength materials. However, the metal carbonate crystals had a disadvantage as material that they were brittle.
Accordingly, under progress is development for composite materials superior both in strength and toughness, in combination of a metal carbonate and an inorganic material and/or an organic material.
Specifically, proposed was a method of preparing saturated aqueous CaCO3 solution and depositing a CaCO3 film on a substrate by using the saturated aqueous CaCO3 solution (see Non-Patent Document 1).
Alternatively, proposed was a method of depositing a carbonate film on an organic matrix, by placing a substrate having an organic matrix coated on the surface and a raw material solution containing a raw carbonate material and an organic polymer in a pressure vessel and introducing CO2 gas into the pressure vessel (see Patent Document 1).
However, the conventional method of using saturated aqueous CaCO3 solution is lower in reactivity, because of limited solubility. As a result, it demands an elongated period of time to form a CaCO3 film and the film formed is also thinner, making it difficult to prepare a large-area CaCO3 film. In addition, to obtain a composite material in a desirable shape, it was necessary to process the composite material having a very hard CaCO3 film. Thus, unfortunately, the conventional method gave only a product that is difficult to process and could not give a composite material in a desirable shape.
Strictly speaking, the material obtained by the conventional method of depositing a carbonate film on the organic matrix is not a composite material. It is only a laminate of a carbonate film and an organic matrix, and is not a composite material in which these components are mixed with each other (see FIG. 2 in Patent Document 1). Patent Document 1 discloses a method of producing a carbonate composite material by depositing a carbonate on the surface and/or in the micropore of the organic matrix. However, because an ionic organic matrix is used, the organic matrix may accumulate by aggregation because of salting out in the presence of a carbonate. Thus unfavorably, it was very difficult to obtain a composite material in any shape and the carbonate was easily localized in the organic matrix. It was thus difficult to obtain a composite material containing the organic matrix and a carbonate dispersed uniformly. It was also difficult to obtain a composite material having desirable properties, such as high hardness and toughness.
Patent Document 1: JP 2004-307262 Unexamined Patent Publication (Kokai)
Non-Patent Document 1: Takashi Kato and two others, Calcium Carbonate-Organic Hybrid Materials, “ADVANCED MATERIALS”, (Germany), Jun. 18, 2002, Vol. 14, No. 12, p. 869-877
An object of the present invention is to provide a solid composite material easily molded into a desirable shape and superior both in hardness and toughness, and a method of producing the same.